Preheat oven to 475°.
Combine the rosemary and garlic. Make several 1/2-inch-deep slits in pork; place about half of rosemary mixture in slits. Rub pork with remaining rosemary mixture; sprinkle with salt and pepper. Place pork on a jelly roll pan coated with cooking spray. Insert a meat thermometer into thickest portion of pork.
Bake at 475° for 20 minutes or until the thermometer registers 160° (slightly pink) or desired degree of doneness. Let stand 5 minutes, and cut into 1/4-inch-thick slices.
Strip rosemary leaves by running your fingertips along the stem in the opposite direction from which the leaves grow.